If UIs today still looked exactly the same as Windows 2.0 or System 7 or CDE people will be bored to death. Aesthetics come and go and come back, it's part of how humanity worked for a few centuries already.
For some of us, the OS isn't a fashion statement, but rather a tool which is to be used to achieve other goals. It shifting around and changing its look is in fact a downside in that context.
I don't think I know any non-tech people who like things changing about. Some tech people like that (I don't), but for the non-techy, it's just another thing they have to relearn for no good reason.
Why do people say that? I am not bored by my Braun alarm clock, neither by my Singer sewing machine or my De Buyer cookware. Why would I be bored by well executed digital desktop designs such as BeOS, AmigaOS or even Windows 2000?
> people will be bored to death
As opposed to what? Be entertained by all the bells and whistles of modern operating systems that have practically unusable user interfaces?
Do I need to be entertained by my butter knife, mop or screwdriver?
I really don't think that "keeping people entertained" is a sensible goal within the context of building software as tools and not software-adjacent Art.
Which is not to say that I would not want a great and polished experience, but that is not equivalent to "being entertained".
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It would be nice if not everything one interacts with would try to get some sort of emotion out of me. Bring back being bored.